The thermal compression tests of Ti80 alloy with bimodal microstructure was conducted at the deformation temperature of 860-980℃ and the strain rate of 0.01~1s^(-1)on the Gleeble-1500 thermal-mechanical simulator. The flow stress and dynamic recrystallization behavior of the alloy during hot deformation were investigated, the critical strain of dynamic recrystallization was determined with the help of the work hardening rate. The results show that dynamic recrystallization is an important softening mechanism during hot deformation of Ti80 alloy, and the critical strain of dynamic recrystallization decreases with increasing temperature and decreasing strain rate. Based on the Z parameter and the improved Avrami equation, the critical strain and kinetics model for dynamic recrystallization of Ti80 alloy were constructed.